Method and apparatus for image forming capable of effectively performing an image fixing process

BACKGROUND

1. Field

This patent specification relates to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming that is capable of effectively performing an image fixing process using a sheet-like-shaped member for forming a heat and pressure nip.

2. Discussion of the Background

FIG. 1 illustrates a typical structure of a background fixing apparatus that is employed in an electrophotographic image forming apparatus to fix a toner image on a recording sheet. As shown in FIG. 1, the background fixing apparatus includes a heat fixing roller <b>1</b> which is provided with a heater <b>2</b> arranged inside for heating and a pressure fixing roller <b>3</b> arranged in pressure contact with the heat fixing roller <b>1</b>. The fixing apparatus further includes a temperature detector <b>4</b> for detecting a surface temperature of the heat fixing roller <b>1</b> heated by the heater <b>2</b>, a guide plate <b>5</b> for guiding a recording sheet into an area between the heat fixing roller <b>1</b> and the pressure fixing roller <b>3</b>, a separation pawl <b>6</b> for separating the recording sheet wrapping around the heat fixing roller <b>1</b> from the heat fixing roller <b>1</b>, and a pair of transfer rollers <b>7</b> arranged in a sheet exit side of the fixing apparatus.

Into this fixing apparatus, a recording sheet having a toner image thereon is transferred and is guided by the guide plate <b>5</b> to a nip area formed between the heat fixing roller <b>1</b> and the pressure fixing roller <b>3</b>. The toner image on the recording sheet is subjected to heat and pressure in the nip area and is fixed on the recording sheet. After that, the recording sheet having the fixed toner image thereon is transferred and is ejected outside the fixing apparatus with the pair of transfer rollers <b>7</b>. As the recording sheet passes through the nip area, toner particles attached to heat fixing roller <b>1</b> are removed by a cleaning pad (not shown).

The surface temperature of the heat fixing roller <b>1</b> is detected by the temperature detector <b>4</b> and, based on the detection result by the temperature detector <b>4</b>, a heat controller (not shown) controls the heating of the surface temperature of the heat fixing roller <b>1</b> with the heater <b>2</b>.

Conventionally, the background fixing apparatus employing a pair of the above-described heat fixing roller <b>1</b> and the pressure fixing roller <b>3</b> generally adopts an infrared heater or a halogen heater as a heating element. However, the pressure fixing roller <b>3</b> has a relatively large heat capacity due to its structure that typically uses a core metal covered with a silicone rubber layer on which a release layer made of polytetrafluoroetylene (e.g., TEFLON) is formed. Because of this large heat capacity, the pressure fixing roller <b>3</b> takes a relatively long time to heat, after the heating of the heat fixing roller <b>1</b> with the heater <b>2</b> is started. This tendency grows with a control developed in recent years with consideration given to energy savings and becomes a major factor causing a failure of the fixing process. Further, this background fixing apparatus has another drawback that the components involved are relatively expensive.

In addition, the background fixing apparatus presses the heater fixing roller <b>1</b> against the pressure fixing roller <b>3</b> with a relatively large force in order to maintain a predetermined width of the nip area, and such large force produces a stress relative to the recording sheet transferred by the heater fixing roller <b>1</b> and the pressure fixing roller <b>3</b>. As a result, the recording sheet may form wrinkles therein. These wrinkles are referred to as a fixing wrinkles.

To attempt to avoid the fixing wrinkles, a fixing apparatus is developed which employs a pressure member having a sheet-like shape in place of the pressure fixing roller <b>3</b> and contacts such pressure member with the heat fixing roller <b>1</b> so as to form a nip area between the pressure member and the heat fixing roller <b>1</b>. In this configuration, the pressure member is prone to be quickly heated due to the sheet-like shape thereof. Also, the nip area is given a predetermined width without causing fixing wrinkles in the recording sheet.

However, the above-mentioned fixing apparatus using the pressure member in the sheet-like shape has a drawback that the nip width is varied and accordingly types of available recording sheets may be limited. That is, in order to arrange the pressure member to press the heat fixing roller, a spring or the like may be disposed at a position opposite to the heat fixing roller relative to the pressure member to press the pressure member against the heat fixing roller. Under such a circumstance, the pressure member may be moved slightly in accordance with the thickness of the recording sheet and, as a result, the nip width may be varied.

SUMMARY

This patent specification describes a novel image fixing apparatus that uses a sheet-like-shaped member. In one example, a novel image fixing apparatus includes a fixing roller, a sheet-like-shaped member, a sheet supporter, and a stopper. The fixing roller includes a heater and is configured to rotate to forward a recording sheet having a toner image. The sheet-like-shaped member is configured to contact the fixing roller to form a nip area with the fixing roller. The sheet supporter is configured to support the sheet-like-shaped member at an upstream side of a bottom surface of the sheet-like-shaped member in a direction in which the recording sheet is transferred. The stopper is configured to stop a free side of the sheet-like-shaped member so that the free side of the sheet-like-shaped member is not lowered from a predetermined position.

The stopper may be configured to be movable, and the image fixing apparatus may further include an adjustment mechanism which is configured to move the stopper to adjust a vertical position of the sheet-like-shaped member.

The stopper may be configured to be an eccentric roller having an eccentric shaft and the adjustment mechanism including a shaft supporter for supporting the eccentric shaft and an adjuster for turning the eccentric shaft.

The eccentric shaft may be configured to have a cross section of a polygonal and the shaft supporter may be configured to have a V-like-shaped portion to be engaged with a corner of the polygon of the eccentric shaft.

The adjuster may be connected to the eccentric shaft and may be configured to have indexes for indicating information associated with turning positions of the eccentric shaft corresponding to vertical positions of the sheet-like-shaped member.

The information indicated by the indexes may include applicable thickness of a recording sheet corresponding to the vertical positions of the sheet-like-shaped member.

The novel image fixing apparatus may further include a moving mechanism configured to move the fixing roller to make contact with the sheet-like-shaped member.

The moving mechanism may include a holding member configured to hold the fixing roller for rotation and a pressing member configured to apply a force to the holding member in a direction toward the sheet-like-shaped member.

The holding member may be provided with a turning shaft at a position different from a rotation axis of the fixing roller so that the holding member is caused to pivot about the turning shaft by the force of the pressing member to make contact with the sheet-like-shaped member.

The moving mechanism may further include an actuating lever configured to switch to a first position to hold the holding member against the force of the pressing member such that the fixing roller is separated from the sheet-like-shaped member and to a second position to release the holding member so that the fixing roller is made in contact with the sheet-like-shaped member, and a stopper provided to the holding member for stopping the actuating lever at the first position.

The sheet-like-shaped member may be made of a rigid and heat-resistant resin.

This patent specification further describes another novel image fixing apparatus. In one example, this novel fixing apparatus includes a plurality of rollers, a sheet-like-shaped member, a holder, and a stopper. The plurality of rollers includes at least one fixing roller containing a heating source. The sheet-like-shaped member contacts the fixing roller, forms a nip area therewith, and is made of a rigid and heat-resistant resin. The holder is configured to hold one side of the sheet-like-shaped member. The stopper is configured to stop a free side of the sheet-like-shaped member such that the free side of the sheet-like-shaped member is not lowered below a predetermined position.

This patent specification further describes a novel method of image forming. In one example, the novel method includes the steps of providing, arranging, supporting, applying, stopping, and transferring. The providing step provides a fixing roller that includes a heater and is rotated to be able to forward a recording sheet having a toner image in a sheet transfer direction. The arranging step arranges a sheet-like-shaped member made of a rigid and heat-resistant material under the fixing roller. The supporting step supports the sheet-like-shaped member at an upstream side of a bottom surface of the sheet-like-shaped member in the sheet transfer direction. The applying step applies a pressure to the fixing roller so that the fixing roller is made to contact under pressure with the sheet-like-shaped member so as to form a nip area therebetween. The stopping step stops a free side of the sheet-like-shaped member so that the free side of the sheet-like-shaped member is not lowered from a predetermined position. The transferring step transfers a recording sheet having a toner image thereon into the nip area in the sheet transfer direction.

This patent specification further describes a novel image forming apparatus. In one example, the novel image forming apparatus includes an image fixing apparatus including a fixing roller, a sheet-like-shaped member, a sheet supporter, and a stopper. The fixing roller includes a heater and is configured to rotate to forward a recording sheet having a toner image. The sheet-like-shaped member is configured to contact the fixing roller to form a nip area with the fixing roller. The sheet supporter is configured to support the sheet-like-shaped member at an upstream side of a bottom surface of the sheet-like-shaped member in a direction in which the recording sheet is transferred. The stopper is configured to stop a free side of the sheet-like-shaped member so that the free side of the sheet-like-shaped member is not lowered from a predetermined position.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic illustration for explaining a structure of a background image fixing apparatus;

FIG. 2 is a side cross-sectional view of an image forming apparatus according to a preferred embodiment;

FIG. 3A is a side cross-sectional view of a fixing unit included in the image forming apparatus of FIG. 2, in a state in which a fixing roller contacts with a sheet-like-shaped member to form a nip area therebetween;

FIG. 3B is a side cross-sectional view of the fixing unit in a state in which the fixing roller is separated from the sheet-like-shaped member;

FIG. 4 is a front cross-sectional view of a stopper stopping the sheet-like-shaped member;

FIG. 5 is another side cross-sectional view of the fixing unit in which the sheet-like-shaped member is settled at the lowest position; and

FIG. 6 is another side cross-sectional view of the fixing unit in which the sheet-like-shaped member is settled at the highest position.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to FIG. 2, a description is made of a facsimile apparatus <b>10</b> as one example of an electrophotographic image forming apparatus according to a preferred embodiment. FIG. 2 is a cross-sectional schematic view of the facsimile apparatus <b>10</b>. As shown in FIG. 2, the facsimile apparatus <b>10</b> includes an optical writing unit <b>11</b>, a photosensitive member <b>12</b>, a process cartridge <b>13</b>, a sheet cassette <b>14</b>, a feed roller <b>15</b>, an image transfer roller <b>16</b>, a pair of sheet transfer rollers <b>17</b>, a sheet ejection tray <b>18</b>, and a fixing unit <b>20</b>. The facsimile apparatus <b>10</b> further includes a document bed <b>40</b>, a close-contact sensor <b>41</b>, a document feed mechanism <b>42</b>, and a document output tray <b>43</b>.

The optical writing unit <b>11</b> produces a laser light beam L modulated in accordance with image data and causes the laser light beam L to scan the photosensitive member <b>12</b> so as to form a latent image thereon. The process cartridge <b>13</b> accommodates the photosensitive member <b>12</b> as well as various components associated with the electrophotographic image processing, and is configured to be detachable from the facsimile apparatus <b>10</b>. The sheet cassette <b>14</b> contains recording sheets which are picked up and fed sheet by sheet by the feed roller <b>15</b>. A toner image on the photosensitive member <b>12</b> based on the latent image is transferred onto the recording sheet by the image transfer roller <b>16</b> which contacts the photosensitive member <b>12</b>. The recording sheet having the toner image thereon is fed to the fixing unit <b>20</b> which fixes the toner image on the recording sheet, and the sheet is ejected to the sheet ejection tray <b>18</b> by the pair of sheet transfer rollers <b>17</b>.

An original document placed on a document bed <b>40</b> is brought to pass by the close-contact sensor <b>41</b> and is ejected to the document output tray <b>43</b>, by the document feed mechanism <b>42</b>. During the time the original document passes by the close-contact sensor <b>41</b>, an image of the original document is optically read by the close-contact sensor <b>41</b>. The image data read by the close-contact sensor <b>41</b> can be treated as a facsimile signal and transmitted to other facsimile machines or the like through a facsimile communications procedure. Alternatively, or in addition, the image data read by the close-contact sensor <b>41</b> in the way described above or input from other facsimile machines into the facsimile apparatus <b>10</b> is handled as input image data and is sent to the optical writing unit <b>11</b>.

The optical writing unit <b>11</b> generates the laser light beam L through modulation in accordance with the input image data and causes the laser light beam L to scan the surface of the photosensitive member <b>12</b>, thereby forming an electrostatic latent image on the surface of the photosensitive member <b>12</b>. The electrostatic latent image is developed into a visual image with toner particles on the photosensitive member <b>12</b>. Such visual image is referred to as a toner image. Then, the toner image formed on the photosensitive member is transferred onto a recording sheet by the image transfer roller <b>16</b>. After a completion of the image transfer, the recording sheet having the toner image thereon is moved to the fixing unit <b>20</b> which applies heat and pressure to the toner image which is unfixed up to this time. With such heat and pressure, the toner image is fixed on the recording sheet. Then, the recording sheet is ejected to the sheet ejection tray <b>18</b> by the pairs of sheet transfer rollers <b>17</b>.

Referring to FIGS. 3A and 3B, an exemplary structure and operations of the fixing unit <b>20</b> are explained in detail. As shown in FIG. 3A, the fixing unit <b>20</b> includes a fixing roller <b>21</b>, a heater <b>22</b>, a sheet-like-shaped member <b>23</b>, a housing <b>24</b>, a transmission gear <b>25</b>, a pressure member (e.g., a spring) <b>26</b>, a sheet supporter <b>27</b>, a first stopper <b>28</b>, an actuator (e.g. a lever) <b>29</b>, and a second stopper <b>30</b>. The housing <b>24</b> includes a supporter <b>24</b><i>a </i>for supporting the fixing roller <b>21</b>, a pivot shaft <b>24</b><i>b </i>for allowing the housing <b>24</b> to pivot about the pivot shaft <b>24</b><i>b, </i>and a pawl <b>24</b><i>c. </i>The transmission gear <b>25</b> transmits a driving force generated by a driving power generator (not shown) to the fixing roller <b>21</b>. The pressure member <b>26</b> presses the fixing roller <b>21</b> against the sheet-like-shaped member <b>23</b>. The sheet supporter <b>27</b> supports the sheet-like-shaped member <b>23</b>. The first stopper <b>28</b> stops or limits bending of the sheet-like-shaped member <b>23</b>.

The actuator <b>29</b> allows the fixing roller <b>21</b> to move between first and second positions, up and down, about pivot <b>24</b><i>b. </i>In the first position, the fixing roller <b>21</b> contacts the sheet-like-shaped member <b>23</b> and a nip area is formed therebetween, as illustrated in FIG. <b>3</b>A. In the second position, the fixing roller <b>21</b> is separated from the sheet-like-shaped member <b>23</b> and no nip area is formed therebetween, as illustrated in FIG. <b>3</b>B. The actuator <b>29</b> has one end engaged with the pawl <b>24</b><i>c </i>of the housing <b>24</b> and another end connected to a driving mechanism (not shown) for driving the actuator <b>29</b> to move the fixing roller <b>21</b> between the first and second positions, as described above. When the actuator <b>29</b> is moved to release the housing <b>24</b>, the housing is moved by the pressure member <b>26</b> and is stopped in the first position with a third stopper (not shown) such that the fixing roller <b>21</b> is brought to push the sheet-like-shaped member <b>23</b> with a pressure of from 1N to 20N at the nip area.

The second stopper <b>30</b> is arranged at a position downstream from the nip area in the direction in which a recording sheet P is transferred and under the sheet-like-shaped member <b>23</b>. When the fixing roller <b>21</b> is moved from the second position to the first position, the side of the sheet-like-shaped member <b>23</b> close to the second stopper <b>30</b> is pressed down by the fixing roller <b>21</b> and is brought into contact with the second stopper <b>30</b>, as illustrated in FIG. <b>3</b>A. That is, the position of the side of the sheet-like-shaped member <b>23</b> at to the second stopper <b>30</b> is regulated by the second stopper <b>30</b>.

The sheet-like-shaped member <b>23</b> may be made of any one of a heat-resistant resin including a rigid fluoride resin or polyimide, a heat-resistant or rigid substrate covered with a fluoride resin, a substrate attached by a metal plate, and a metal plate made of a rigid iron, copper, or the like. The above-mentioned substrate may include air bubbles, with consideration given to a thermal storage capability of the substrate.

Further, it is also possible to form the sheet-like-shaped member <b>23</b> using a common material used for the cases, for example, of the fixing unit, such as a polycarbonate resin, an ABS (acrylonitrile-butadiene-styrene) resin, or the like, having a sufficient heat-resistant nature. Also, it is possible to form the sheet-like-shaped member <b>23</b> integrated with the sheet supporter <b>27</b> into a single component. By these arrangements, the number of components can be reduced.

The recording sheet P carrying the transferred toner image is forwarded to the fixing unit <b>20</b> in which, by this time, the fixing roller <b>21</b> is heated up to a predetermined fixing temperature by the heater <b>22</b> and is moved to the first position by the actuator <b>29</b> to make contact with the sheet-like-shaped member <b>23</b>. Also, the fixing roller <b>21</b> is driven to rotate to forward the recording sheet P. Under such conditions of the fixing unit <b>20</b>, the recording sheet P is subjected to the fixing process with heat and pressure in the nip area between the fixing roller <b>21</b> and the sheet-like-shaped member <b>23</b>.

FIG. 4 is a front view of the second stopper <b>30</b> of the fixing unit <b>20</b>. The second stopper <b>30</b> includes an eccentric roller <b>31</b> which has a rotary shaft <b>32</b> at a position eccentric relative to the center axis of the eccentric roller <b>31</b>. The rotary shaft <b>32</b> has a square cross-sectional profile and is arranged at a position such that one of two diagonal lines in the square of the cross section intersects the center axis of the eccentric roller <b>31</b>. The second stopper <b>30</b> further includes shaft supporters <b>33</b> which are arranged at positions under both edge sides of a movable side of the sheet-like-shaped member <b>23</b>. Each of the shaft supporters <b>33</b> has a portion of a 90-degree V-like shape for carrying and supporting the rotary shaft <b>32</b>.

When the eccentric roller <b>31</b> is installed with the rotary shaft <b>32</b> fitting on the shaft supporters <b>33</b>, the movable side of the sheet-like-shaped member <b>23</b> contacts with the eccentric roller <b>31</b>.

The second stopper <b>30</b> further includes a control knob <b>34</b> which is provided at one end of the rotary shaft <b>32</b> of the eccentric roller <b>31</b> and which uses the rotary shaft <b>32</b> as the center axis thereof. This control knob is manipulated by an operator.

When the eccentric roller <b>31</b> is in a position such that a corner of the cross sectional square of the rotary shaft <b>32</b> closest to the center axis of the eccentric roller <b>31</b> is supported by the shaft supporters <b>33</b>, the sheet-like-shaped member <b>23</b> is brought to a position closest to the rotary shaft <b>32</b>, as illustrated in FIG. <b>5</b>. The control knob <b>34</b> can be rotated by 90 degrees and the next corner of the cross sectional square of the rotary shaft <b>32</b> is stopped with a click by an engagement with the shaft supporters <b>33</b>. During this 90-degree rotation, the eccentric roller <b>31</b> lifts the sheet-like-shaped member <b>23</b> and, as a result, the width of the nip area between the fixing roller <b>21</b> and the sheet-like-shaped member <b>23</b> is increased. When the control knob <b>34</b> is further rotated by 90 degrees and the next corner of the cross sectional square of the rotary shaft <b>32</b> is engaged with the shaft supporters <b>33</b>, the sheet-like-shaped member <b>23</b> is brought to a position most distant from the rotary shaft <b>32</b>, as illustrated in FIG. <b>6</b>. Thus, the nip area has the maximum width. In this way, the width of the nip area can be controlled by the control knob <b>34</b>.

Indications for selective sheet types, environmental conditions, and the like are provided to the control knob <b>34</b> so that by turning the control knob <b>34</b> the operator can change the engagement of the shaft supporters <b>33</b> with one of the four corners of the cross-sectional square of the rotary shaft <b>32</b> suitable for the sheet type or environmental conditions desired, for example. In the present embodiment, the control knob <b>34</b> is provided with three indicators “THICK” for a thick sheet, “NORMAL” for a normal sheet, and “THIN” for a thin sheet. When the operator turns the control knob <b>34</b> to select “THICK” to use a thick sheet, the sheet-like-shaped member <b>23</b> is moved down to the lowest position. Likewise, when the control knob <b>34</b> is turned to select “NORMAL,” the sheet-like-shaped member <b>23</b> is moved to the middle position and when the control knob <b>34</b> is turned to select “THIN,” the sheet-like-shaped member <b>23</b> is moved to the highest position.

With the above-described structure, the eccentric roller <b>31</b> contacts the free edge side of the sheet-like-shaped member <b>23</b> and consequently functions as a stopper for stopping or limiting downward motion of the sheet-like-shaped member <b>23</b>. That is, the eccentric roller <b>31</b> regulates the vertical movement of the sheet-like-shaped member <b>23</b>, particularly when the recording sheet is brought to pass through the nip area, so as to stably hold the nip width. Further, the operator can adjust the nip width according to the type of the sheet by turning the control knob <b>34</b>, that is, the eccentric roller <b>31</b> is turned so as to shift the sheet-like-shaped member <b>23</b> to a suitable one of the predetermined vertical positions.

As described above, the nip width is adjusted by the turn of the eccentric roller <b>31</b> to change the vertical position of the sheep-like-shaped member <b>23</b>. However, the adjustment of the nip width is not so limited. For example, a different stopper may be provided at the free edge side of the sheet-like-shaped member <b>23</b>, configured to be slidable in vertical and horizontal directions. With such a structure, the nip width can be adjusted by a movement of the stopper.

In addition, since the sheet-like-shaped member <b>23</b> has a part which contacts with and is rubbed by the rotating fixing roller <b>21</b> in the nip area, such part may be prone to be worn and/or deformed. However, the wearing and/or deformation of the sheet-like-shaped member <b>23</b> may be reduced by the configuration in which the sheet-like-shaped member <b>23</b> can be separated from the fixing roller <b>21</b> with the actuator <b>29</b>.

Further, the first stopper <b>28</b> is provided under the sheet-like-shaped member <b>23</b> with a slight gap from the rear surface of the sheet-like-shaped member <b>23</b>. With this gap, it becomes possible to avoid deformation of the sheet-like-shaped member <b>23</b> in the nip area, which may be caused when the recording sheet is jammed while passing between the fixing roller <b>21</b> and the sheet-like-shaped member <b>23</b>.

In addition, when a sheet jam occurs in the nip area, the jammed-sheet may easily be removed from the nip area after the fixing roller <b>21</b> is separated from the sheet-like-shaped member <b>23</b> with the actuator <b>29</b>. To separate the fixing roller <b>21</b> and the sheet-like-shaped member <b>23</b> from each other, it is also possible to move the sheet-like-shaped member <b>23</b>. In this case, however, the second stopper <b>30</b> is required to be moved away.

Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.

This patent specification is based on Japanese patent application No. JPAP2001-188059 filed on Jun. 21, 2001 in the Japanese Patent Office, the entire contents of which are incorporated by reference herein.